Many drugs are capable of penetrating the skin and thereby the general circulatory system where they act systemically. The advantages of administering drugs this way are the elimination of the uncontrollable factors of gastrointestinal absorption, the reduction of the metabolism by avoiding the first liver passage, the avoidance of initial high blood concentrations and attainment of a more constant blood level over a longer period of time.
Various transdermal sustained release systems for are known which use polymers as part of the transdermal device. U.S. Pat. No. 4,409,206 is directed to a pharmaceutical preparation which is a film of a polyacrylate which swells in water and contains an active substance in amorphous form. Useful polyacrylate materials are polymers or copolymers of acrylic acid or methacrylic acid, alkyl esters thereof, and acrylonitrile.
U.S. Pat. No. 4,291,015 covers a polymeric diffusion matrix containing a vasodilator which comprises from 2 to 60% of a polar plasticizer, 2 to 15% of a matrix component such as polyvinylalcohol, and from 2 to 10% of a water-soluble polymer with hydration sites, e.g., polyvinylpyrrolidone.
U.S. Pat. No. 3,966,902 pertains to a polymer complex carrier and an active ingredient entrapped therein. The complex is in part a monomer with a hydrophilic function and contains aluminum, zinc, or zirconium metal bound in complex form.
Polymeric substrates that are soluble in water are not suitable for long-term transdermal application. The present invention provides a novel transdermal release system for both hydrophilic and hydrophobic drugs. The polymer swells but does not dissolve in water. It provides a delivery system which is simple and inexpensive to produce, which ensures a reproducible, controlled release with low temperature-dependence and a constant rate up to a high dose, and also permits variation of the rate of release within wide limits.
These characteristics provide for excellent oral controlled release forms as well.